City Light and partners use trees to “plant” a new South Fork Tolt River

Tipped trees along the South Fork Tolt River

This summer, City Light and its agency partners, including the Tulalip Tribes, NOAA Fisheries, U.S. Fish and Wildlife Service, Seattle Public Utilities and the Washington Department of Fish and Wildlife, continued to revitalize the South Fork Tolt River. In early July, the group placed 117 trees throughout the river using a Chinook helicopter.

These trees were used to create large jams that should remain in the river for a long time to come. The trees were available for salvage from other projects requiring tree clearing close to the river. This collaborative project was funded through mitigation dollars as part of the City’s South Fork Tolt Hydroelectric Project Federal Energy Regulatory Commission license.

A Chinook helicopter towing tipped trees to be placed in the river

City Light utilized Light Detection and Ranging, or LIDAR, a remote-sensing method that uses light in the form of a pulsed laser to measure ranges to the Earth, and aerial photography to assist in determining where to place trees in the river strategically. The team placed trees into the river to create deflector, midchannel and apex jams. This approach forms discrete structures at specific locations and uses natural processes, causing interactions with the floodplain to create and maintain new stream habitats. These revitalized habitats are especially vital for the endangered Chinook salmon and steelhead populations and the numerous other fish and wildlife species that pass through this area. 

A Lidar map of the South Fork Tolt River. The “A” represents the log jam in the photograph below.

“This multi-agency partnership focused on building jams to increase channel complexity, activating side channels and trapping gravel. We were striving to create more of all things important for fish that spawn and rear in this river, including fast, slow, deep and shallow water and cover for them to hide. We chose areas that could create reach-level geomorphic change, expanding flows into the floodplain,” Liz Ablow, Strategic Advisor with City Light, said. “When you look back at the history of these rivers, there were old-growth trees and a natural cycle of large wood falling into the river to create this kind of change. Historically, these areas were logged, losing the natural recruitment of large trees. With this project, we can boost the river while trees along the river grow back. It’s been really exciting to have such a great opportunity. It is not every day you get to treat miles of river in hopes of bringing it closer to what it once was.”

This work was the second phase of this project which initially began in Fall 2020. All told, City Light and its partner agencies placed 298 trees weighing in at 2.5 million pounds along a six-mile span of the South Fork Tolt River west of the South Fork Tolt Reservoir. For Derek Marks, Timber Fish and Wildlife Manager with the Tulalip Tribes of Washington, this work is monumental for the future of the South Fork Tolt. 

“This is the kind of project that you get out of bed for,” Marks explained. “We, along with the generations that follow us, will benefits from this work for years to come. We are proud to work with groups like Seattle City Light and our other partners to improve this vital river and watershed.” 

Next winter, the team plans to have more aerial photos taken to identify where these trees have settled and where geomorphic change has been made.